This invention relates to a novel epoxy resin composition which is curable at room temperature. The composition may find use, for example, in air-drying paints, adhesives and potting compounds of electric and electronic parts.
Epoxy resins are known to have excellent heat-resistant, adhesive, antichemical, electrical, mechanical and other properties and, therefore have extensively been used in various fields as adhesives, coatings, sealants, insulating materials, casting and molding compounds and the like.
Two systems are known to harden or cure the epoxy resins; one using a polyamine or polycarboxylic acid or anhydride hardener and the other being a self-polymerization system containing a cationic or anionic polymerization initiator generally referred to as "curing catalyst".
In our Japanese Patent Application No. 310001/1990 corresponding to U.S. Ser. No. 07/791,503, a room-temperature curable resin composition comprising (a) an acrylic polymer having a plurality of alicyclic epoxide functions, and (b) as a curing catalyst a Bronsted acid, a Lewis acid or an amine salt of superacid.
Our Japanese Patent Application No. 125055/1991 corresponding to U.S. Ser. No. 07/872,699 discloses a similar epoxy resin composition containing a substituted urea salt of superacid as a curing catalyst.
It has been found that these compositions are not fully satisfactory in certain properties such as water resistance.
U.S. Pat. Nos. 4,772,672, 4,923,930 and 4,923,945 disclose a low-temperature curable resin composition comprising a polymer having an oxirane ring and an alkoxysilyl group in the molecule and as a curing catalyst an aluminum or zirconium chelate. The curing reaction of this composition, however, takes a relatively long period of time at room temperature.
A need exists, therefore, for a room-temperature curable epoxy resin composition which exhibits improved water resistance and other properties compared with the above-discussed known compositions.